Set of 5. Dual ring patented technology. Specially designed stem provides quiet mobility on all floor surfaces. Eliminates black powder residue created by metal-to-metal friction. Extended life cycle on stem fastener. Perfect for hospitals, libraries, schools and offices anywhere quiet is necessary. Weight capacity: 100 lbs.. Made from nylon. 5.50 in. W x 3 in. D x 6.75 in. H (1.98 lbs.) Remove caster from leg of chair base. Match the stem of the caster to diagram. Select the correct length and diameter. (Tops of stems can be flat or roundedeither will fit.). Determine if caster is to be used on chair mats, hard floors or carpeting. Choose soft wheel casters for use on chair mats, linoleum (vinyl), and hard floors; hard wheel casters for carpeting.